Device containing compound having indolocarbazole moiety and divalent linkage

ABSTRACT

An electronic device including a compound comprising at least one type of an optionally substituted indolocarbazole moiety and at least one divalent linkage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending U.S.application Ser. No. 11/280,795, tiled on Nov. 16, 2005, the disclosureof which is totally incorporated herein by reference.

Yuning Li et al., U.S. application Ser. No. 11/280,552, filed on thesame day as the present application, titled “COMPOUND HAVINGINDOLOCARBAZOLE MOIETY AND DIVALENT LINKAGE.”

Beng S. Ong et al., U.S. application Ser. No. 10/865,620, filed Jun. 10,2004, titled “DEVICE WITH SMALL MOLECULAR THIOPHENE COMPOUND HAVINGDIVALENT LINKAGE.”

Yiliang Wu et al., U.S. application Ser. No. 11/167,485, filed Jun. 27,2005, titled “THIN FILM TRANSISTORS INCLUDING INDOLOCARBAZOLES.”

Beng S. Ong et al., U.S. application Ser. No. 11/167,512, filed Jun. 27,2005, titled “COMPOUND WITH INDOLOCARBAZOLE MOIETIES AND DEVICESCONTAINING SUCH COMPOUND.”

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with United State Government support underCooperative Agreement No. 70NANBOH3033 awarded by the National Instituteof Standards and Technology (NIST). The United State Government hascertain rights in the invention.

BACKGROUND OF THE INVENTION

Organic electronics has been an intense research topic over the last twodecades or so because of their enormous commercial potential. Someillustrative organic electronic devices are diodes, organic thin filmtransistors, and organic photovoltaics. One of the key components inthese devices is organic semiconductors which have received extensiveresearch and development efforts. In the field of organic electronics,organic thin film transistors (OTFTs) have in recent years attractedgreat attention as a low-cost alternative to mainstream amorphoussilicon-based transistors for electronic applications. OTFTs areparticularly suited for applications where large-area circuits (e.g.,backplane electronics for large displays), desirable form factors andstructural features (e.g., flexibility for “electronic paper”), andaffordability (e.g., ultra low cost for ubiquitous radio frequencyidentification tags) are essential.

Organic semiconductors are typically based on: (1) acenes such astetracene, pentacene and their derivatives, (2) thiophenes such asoligothiophenes and polythiophenes, (3) fused-ring thiophene-aromaticsand thiophene-vinylene/arylene derivatives. Most of these semiconductorsare either insoluble in common organic solvents or sensitive to air, andare therefore not suitable for fabricating low-cost OTFTs via liquidpatterning and deposition processes under ambient conditions. There istherefore a critical need addressed by embodiments of the presentinvention to develop liquid-processable and air stable organicsemiconductor compounds to enable low-cost OTFTs.

The following documents provide background information:

Christos D. Dimitrakopoulos et al., “Organic Thin Film Transistors forLarge Area Electronics,” Adv. Mater., Vol. 14, No. 2, pp. 99-117 (2002).

Salem Wakim et al., “Organic Microelectronics: Design, Synthesis, andCharacterization of 6,12-Dimethylindolo[3,2-b]Carbazoles,” Chem. Mater.Vol. 16, No. 23, pp. 4386-4388 (published on web Jul. 7, 2004).

Nan-Xing Hu et al.,“5-11-Dihydro-5,11-di-1-naphthylindolo[3,2-b]carbazole: Atropisomerismin a Novel Hole-Transport Molecule for Organic Light-Emitting Diodes,”J. Am. Chem. Soc., Vol. 121, pp. 5097-5098 (1999).

Ong et al., U.S. Pat. No. 6,949,762

Hu et al., U.S. Pat. No. 5,942,340.

Hu et al., U.S. Pat. No. 5,952,115.

Hu et al., U.S. Pat. No. 5,843,607.

SUMMARY OF THE DISCLOSURE

In embodiments, there is provided a compound comprising at least onetype of an optionally substituted indolocarbazole moiety and at leastone divalent linkage.

In further embodiments, there is provided a small molecule compoundcomprising at least one type of an optionally substitutedindolocarbazole moiety and at least one divalent linkage.

In other embodiments, there is provided a polymer comprising at leastone type of repeat unit comprising at least one type of an optionallysubstituted indolocarbazole moiety and at least one divalent linkage.

In embodiments, there is provided an electronic device comprising acompound comprising at least one type of an optionally substitutedindolocarbazole moiety and at least one divalent linkage.

In further embodiments, there is provided an electronic devicecomprising a small molecule compound comprising at least one type of anoptionally substituted indolocarbazole moiety and at least one divalentlinkage.

In other embodiments, there is provided an electronic device comprisinga polymer comprising at least one type of repeat unit comprising atleast one type of an optionally substituted indolocarbazole moiety andat least one divalent linkage.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects of the present invention will become apparent as thefollowing description proceeds and upon reference to the followingfigures which are representative embodiments:

FIG. 1 represents a first embodiment of the present invention in theform of an OTFT;

FIG. 2 represents a second embodiment of the present invention in theform of an OTFT;

FIG. 3 represents a third embodiment of the present invention in theform of an OTFT; and

FIG. 4 represents a fourth embodiment of the present invention in theform of an OTFT.

Unless otherwise noted, the same reference numeral in different Figuresrefers to the same or similar feature.

DETAILED DESCRIPTION

The present compound (“Compound”) encompasses polymers and smallmolecule compounds. As used herein, a “polymer” includes one, two, ormore types of repeat units. In embodiments of the “polymer,” each typeof repeat unit has any suitable number of repeat units ranging forexample from 2 to about 2000, or from about 5 to about 1000. Inembodiments of the “polymer,” the number of repeat units regardless oftype (that is, for all types) ranges for example from 2 to about 2000,or from about 5 to about 1000. An “oligomer” is a subset of a “polymer”having a small number of repeat units where the “oligomer” may be forexample a dimer, trimer, and the like.

The repeat unit is the fundamental recurring unit of a polymer. Theconnection of the repeat units in the polymer may be identical, in thecase of a regular polymer, or may be not identical, in the case of anirregular polymer, with respect to directional sense. Whether a repeatunit A is considered the same type or a different type as another repeatunit B is independent of directional sense when repeat unit A and repeatunit B are in the polymer. For instance, regiorandom poly(3-hexylthiophene) is considered to have only one type of repeat unit. Asanother example, Xinnan Zhang et al., “Alkyl-SubstitutedThieno[3,2-b]thiophene Polymers and Their Dimeric Subunits,”Macromolecules, Vol. 37, pp. 6306-6315 (published on web Jul. 30, 2004),discloses a regiorandom poly(3-alkylthieno[3,2-b]thiophene) which isconsidered to have only one type of repeat unit.

As used herein, the phrase “small molecule compound” refers to acompound without a repeat unit regardless of its molecular weight. Thus,a compound having a low, medium, or high molecular weight but without arepeat unit would be considered a “small molecule compound” for thepresent purposes.

In embodiments, the Compound is a molecular compound. The phrase“molecular compound” refers to any “polymer” and “small moleculecompound” having a specific molecular weight rather than an averagemolecular weight. While a “small molecule compound” is generally also a“molecular compound” with a specific molecular weight, a “polymer” canhave an average molecular weight or a specific molecular weightdepending on whether the “polymer” has predominantly molecules with thesame number of repeat units (resulting in a specific molecular weight)or a mixture of molecules with different numbers of repeat units(resulting in an average molecular weight).

In the Compound, there is one type, two types, three types, or more ofthe optionally substituted indolocarbazole moiety and of the divalentlinkage. Dissimilarity in any manner can create different “types”. Forexample, a difference in any one or more of the following representativefactors creates different “types” of the indolocarbazole moiety and ofthe divalent linkage in the Compound: (a) whether there is substitution;(b) the type, position and/or number of substituent(s); and (c) the typeof the indolocarbazole for example the illustrative structures A to G asshown thereafter.

The phrase “at least one divalent linkage” refers to the divalentlinkage(s) without regard to type. There can be one, two, or more typesof divalent linkage(s) present in the Compound.

In embodiments, the Compound includes a number of the optionallysubstituted indolocarbazole moiety regardless of type ranging forexample from 2 to 1000 and a number of the at least one divalent linkageregardless of type ranging for example from 1 to 500. In embodiments,each type of the optionally substituted indolocarbazole moiety includesa number of indolocarbazole moiety ranging for example from 1 to 1000.In embodiments, each type of the divalent linkage includes a number ofthe divalent linkage ranging for example from 1 to 500. In embodimentswhere the Compound is a small molecule compound, the number of theoptionally substituted indolocarbazole moiety regardless of type rangesfor example from 2 to 30 or from 2 to 10; and the number of the at leastone divalent linkage regardless of type ranges for example from 1 to 15or from 1 to 5.

In embodiments where the Compound is a polymer, the number of theoptionally substituted indolocarbazole moiety ranges for example from 1to 6 for each type of the repeat unit; and the number of the at leastone divalent linkage ranges for example from 1 to 3 for each type of therepeat unit.

The indolocarbazole moiety of the Compound is unsubstituted orsubstituted with one or more substituents in any suitable substitutionpattern. For substituted embodiments of the indolocarbazole moiety, thesubstitution can be for example the following: (1) one or more nitrogensubstitutions (that is, substitution(s) at the nitrogen atoms) with noperipheral substitution; (2) one or more peripheral substitutions withno nitrogen substitution; or (3) one or more nitrogen substitutions andone or more peripheral substitutions. In embodiments, all the nitrogenatoms of the indolocarbazole moiety are substituted with the same ordifferent substituents, with the indolocarbazole moiety being optionallyperipherally substituted. In embodiments, the indolocarbazole moiety isnitrogen substituted (and optionally peripherally substituted) whereinthe one or more nitrogen substituents are independently selected fromthe group consisting of a hydrocarbon group and a heteroatom-containinggroup, or a mixture thereof. In embodiments, the indolocarbazole moietyis peripherally substituted (and optionally nitrogen substituted)wherein the one or more peripheral substituents are independentlyselected from the group consisting of a hydrocarbon group, aheteroatom-containing group, and a halogen, or a mixture thereof.

The phrases “peripherally substituted” and “peripheral substitution”refer to at least one substitution (by the same or differentsubstituents) on any one or more aromatic rings of the indolocarbazolemoiety regardless whether the aromatic ring is a terminal aromatic ringor an internal aromatic ring (that is, other than at a terminalposition).

In embodiments, the indolocarbazole moieties of the Compound areindependently selected from the group consisting of structures (A), (B),(C), (D), (E), (F), and (G), or a mixture thereof.

wherein for each of the structures (A) through (G), each R isindependently selected from a group consisting of a hydrogen, ahydrocarbon group and a heteroatom-containing group (that is, eachnitrogen atom can have the same or different R), wherein each of thestructures (A) through (G) is optionally peripherally substituted by oneor more substituents selected from the group consisting of a hydrocarbongroup, a heteroatom-containing group, and a halogen, or a mixturethereof.

In embodiments, each divalent linkage is “conjugated” or“non-conjugated” which indicates the nature of the backbonestructure(s); it is understood that any optional substituent(s) on thebackbone structure(s) may or may not be “conjugated.” Representativeexamples of a “non-conjugated” divalent linkage include an oxygen atomand an alkylene containing for instance one to about ten carbon atoms.In embodiments, each divalent linkage may be selected for example fromthe group consisting of the following structural units which areoptionally substituted:

and a combination thereof (“combination” referring to coupling of two ormore of the depicted structures such as for instance the double bondstructure coupled to any of the aromatic structures),wherein X is selected from the group consisting of C(R′R″), O, S, Se,NR′, and Si(R′R″), and wherein R′ and R″ are independently selected fromthe group consisting of a hydrocarbon group, a heteroatom-containinggroup, a halogen and a mixture thereof; and Y is a carbon atom or anitrogen atom.

Each divalent linkage is unsubstituted or substituted with one or moresubstituents in any suitable substitution pattern. For substitutedembodiments of the divalent linkage(s), the substituent(s) can beindependently selected from the group consisting of a hydrocarbon group,a heteroatom-containing group, a halogen and a mixture thereof.

In embodiments, each divalent linkage comprises one, two, or moreoptionally substituted thienylene units, each thienylene unit being thesame or different from each other and of representative structure (I)

where R₁ is independently selected from a hydrocarbon group (such asthose described herein for the optionally substituted indolocarbazolemoiety), a heteroatom-containing group (such as those described hereinfor the optionally substituted indolocarbazole moiety), and a halogen,and where m is 0, 1, or 2. Covalent bondings to other part or moietiesof the Compound are not shown in structure (I). It is understood thateach thienylene unit will have covalent bondings, preferably at 2 and 5positions, when incorporated into the Compound.

A divalent linkage is different from a substituent of theindolocarbazole moiety. Substituents are bonded to the indolocarbazolemoiety via a single covalent bond. On the other hand, the divalentlinkage is bonded in a divalent manner at two positions to for instancetwo indolocarbazole moieties. For example, the bithienylene between thetwo indolocarbazole moieties is considered as the divalent linkage ofthe Compound (1), while the 5-hexyl-thienyl groups at both ends of theCompound (1) are considered as substituents of the indolocarbazolemoiety. Similarly, the biphenylene in the repeat unit of the polymer(17) is considered as the divalent linkage (“biphenylene” for polymer 17refers to the two phenylene moieties between adjacent indolocarbazolemoieties; thus, in the repeat unit for polymer (17), two biphenylenesare coupled to the indolocarbazole moiety but only one phenylene moietyof each biphenylene is depicted), while the 4-octylphenyl groups at thenitrogen positions are considered as substituents of the indolocarbazolemoiety. For Compound (1) and Compound (17), the biphenylene could alsobe viewed as two divalent linkages rather than a single divalentlinkage. In embodiments, it is generally immaterial whether to view thebiphenylene as a single divalent linkage or two divalent linkages. Inembodiments, however, one can consider the moieties at issue to be asingle divalent linkage if the chemical nomenclature indicates such aview is appropriate. In embodiments, one can consider all the moietiesbetween adjacent indolocarbazole moieties to be a single divalentlinkage, particularly for instance when the present claims recite “onlyone divalent linkage.”

The hydrocarbon group of the optional substituent(s) for the Compound(both the optional substituent(s) of the indolocarbaozle moiety and theoptional substitutent(s) of the divalent linkage) contains for examplefrom 1 to about 50 carbon atoms, or from 1 to about 30 carbon atoms, andmay be for example a straight chain alkyl group, a branched alkyl group,a cyclic aliphatic group, an aryl group, an alkylaryl group, and anarylalkyl group. Representative hydrocarbon groups include for examplemethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, cyclopentyl,cyclohexyl, cycloheptyl, and isomeric forms thereof.

The heteroatom-containing group of the optional substituent(s) for theCompound (both the optional substituent(s) of the indolocarbaozle moietyand the optional substitutent(s) of the divalent linkage) has forexample 2 to about 200 atoms, or from 2 to about 100 atoms) and may befor example a nitrogen-containing group, an alkoxy group, a heterocyclicgroup, an alkoxyaryl, an arylalkoxy, and a halogenated hydrocarbon(where the halogen is for example fluorine, bromine, chlorine, oriodine, or a mixture thereof). Representative heteroatom-containinggroups include for example fluoroalkyl, fluoroaryl, cyano, nitro,carbonyl, carboxyl ate, amino (optionally substituted with one or twosubstituents such as for example a hydrocarbon group described herein),and alkoxy (having for example 1 to about 18 carbon atoms). Inembodiments, the heteroatom-containing group is independently selectedfrom the group consisting of fluoroalkyl (having for example 1 to about18 carbon atoms), fluoroaryl, cyano, nitro, carbonyl, carboxylate,alkoxy (having for example 1 to about 18 carbon atoms), and amino(optionally substituted with one or two substituents such as for examplea hydrocarbon group described herein), or a mixture thereof. Inembodiments, the heteroatom-containing group is an optionallysubstituted carbazole group.

The halogen of the optional substituent(s) for the Compound (both theoptional substituent(s) of the indolocarbaozle moiety and the optionalsubstitutent(s) of the divalent linkage) is for example fluorine,bromine, chlorine, or iodine, or a mixture thereof).

The Compound may be a p-type semiconductor, n-type semiconductor orambipolar semiconductor. The type of the semiconducting of the Compounddepends very much on the nature of the substituents. Substituents whichpossess an electron donating property such as alkyl, alkoxy, aryl, andamino groups, when present in the Compound, may render the Compound ap-type semiconductor. On the other hand, substituents which are electronwithdrawing such as cyano, nitro, fluoro, fluorinated alkyl, andfluorinated aryl groups may transform the Compound into the n-typesemiconductor.

Illustrative embodiments of the Compound (involving small moleculecompounds) are:

Further embodiments of the Compound (involving polymers) are:

where n ranges for example from 2 to about 2000.

The Compound can be prepared for instance by an appropriate couplingreaction of an optionally substituted indolocarbazole (a singleoptionally substituted indolocarbazole or a mixture of two or moredifferent optionally substituted indolocarbazoles in any suitableratios) with a divalent linkage precursor (e.g., dibronic acids inSchemes 1 and 2). For example, Compound (1), (2), and (9) through (12)can be synthesized via Suzuki coupling reaction of 2- or3-bromo-5,11-didodecylinodolo[3,2-b]carbazole with diboronic acids asshown in Scheme 1.

In embodiments, a polymeric Compound can be, for example, prepared bycopolymerizing a difunctional monomer comprising an optionallysubstituted indolocarbazole with divalent linkage precursor (e.g., adifunctional monomer comprising an unsaturated compound) or polymerizingof appropriate functionalized monomer of an optionally substitutedindolocarbazole (the functionalized monomer is functionalized with adivalent linkage precursor) as represented in Schemes 2 and 3respectively. For example, polymer (13) through (18) can be prepared viaSuzuki coupling polymerization of 3,9- or2,8-dibromo-5,11-didodecylindolo[3,2-b]carbazole with diboronic acids(Scheme 2). Alternatively, polymer (13) can be prepared via oxidativecoupling polymerization of2,8-bis(2-thienyl)-5,11-didodecylindolo[3,2-b]carbazole with FeCl₃(Scheme 3).

The Compound may be used for any suitable applications. In embodiments,the Compound may be used as a semiconductor for electronic devices suchas for example diodes, thin film transistors, and photovoltaics.

Any suitable techniques may be used to form a semiconductor layercontaining the Compound. One such method for small molecular compoundsis by vacuum evaporation at a vacuum pressure of about 10⁻⁵ to 10⁻⁷ torrin a chamber containing a substrate and a source vessel that holds theCompound in powdered form. Heat the vessel until the Compound sublimesonto the substrate. The performance of the films containing the Compoundmay depend on the rate of heating, the maximum source temperature andsubstrate temperature during the evaporation process. In embodiments,liquid deposition techniques may also be used to fabricate thesemiconductor layer comprised of the Compound, particularly thepolymeric compounds. Liquid deposition techniques refer to for examplespin coating, blade coating, rod coating, screen printing, ink jetprinting, stamping and the like. Specifically, the Compound can bedissolved in a suitable solvent of for example tetrahydrofuran,dichloromethane, chlorobenzene, toluene, and xylene to form a solutionat a concentration of about 0.1% to about 10%, particularly about 0.5%to about 5% by weight, and then used in liquid deposition. Illustrativedeposition by spin coating can be carried out at a spin speed of about500 to about 3000 rpm, particularly about 1000 to about 2000 rpm for aperiod of time of about 5 to about 100 seconds, particularly about 30 toabout 60 seconds at room temperature or an elevated temperature to forma thin film on a suitable substrate such as silicon wafer, glass, orplastic film.

The semiconductor layer may be predominantly amorphous, liquidcrystalline or predominantly crystalline in nature, depending on theCompound and processing conditions. The semiconductor layer can becharacterized by common characterization techniques such as X-raydiffraction, atomic force microscopy, optical microscopy, etc. Forexample, a predominantly amorphous layer usually shows broad X-raydiffraction peaks, while a predominantly crystalline layer generallyexhibits sharp X-ray diffraction peaks. The degree of crystallinity of asemiconductor layer can be calculated from the integrated area ofdiffraction peaks. In embodiments, the phrase “predominatelycrystalline” indicates that the crystallinity of the semiconductor layeris for example larger than about 50%, larger than about 80%, or largerthan about 90%.

Depending on the nature of the Compound, a predominantly crystallinesemiconductor layer can be formed by a number of techniques. Forexample, a predominantly crystalline semiconductor layer can be formedby vacuum evaporation of the Compound onto a substrate holding at anelevated temperature of for example about 50° C. to about 120° C. Inanother technique, a predominantly crystalline semiconductor layer canbe achieved by liquid deposition followed by controlled solventevaporation and optionally post-deposition annealing at an elevatedtemperature of for example about 80° C. to about 250° C.

The representative use of Compound as a semiconductor in electronicdevices is illustrated herein using thin film transistors.

In FIG. 1, there is schematically illustrated an OTFT configuration 10comprised of a substrate 16, in contact therewith a metal contact 18(gate electrode) and a layer of a gate dielectric layer 14 on top ofwhich two metal contacts, source electrode 20 and drain electrode 22,are deposited. Over and between the metal contacts 20 and 22 is anorganic semiconductor layer 12 as illustrated herein.

FIG. 2 schematically illustrates another OTFT configuration 30 comprisedof a substrate 36, a gate electrode 38, a source electrode 40 and adrain electrode 42, a gate dielectric layer 34, and an organicsemiconductor layer 32.

FIG. 3 schematically illustrates a further OTFT configuration 50comprised of a heavily n-doped silicon wafer 56 which acts as both asubstrate and a gate electrode, a thermally grown silicon oxide gatedielectric layer 54, and an organic semiconductor layer 52, on top ofwhich are deposited a source electrode 60 and a drain electrode 62.

FIG. 4 schematically illustrates an additional OTFT configuration 70comprised of substrate 76, a gate electrode 78, a source electrode 80, adrain electrode 82, an organic semiconductor layer 72, and a gatedielectric layer 74.

The composition and formation of the semiconductor layer are describedherein.

The semiconductor layer has a thickness ranging for example from about10 nanometers to about 1 micrometer with a preferred thickness of fromabout 20 to about 200 nanometers. The OTFT devices contain asemiconductor channel with a width W and length L. The semiconductorchannel width may be, for example, from about 1 micrometers to about 5millimeters, with a specific channel width being about 5 micrometers toabout 1 millimeter. The semiconductor channel length may be, forexample, from about 1 micrometer to about 1 millimeter with a morespecific channel length being from about 5 micrometers to about 100micrometers.

The substrate may be composed of for instance silicon, glass plate,plastic film or sheet. For structurally flexible devices, a plasticsubstrate, such as for example polyester, polycarbonate, polyimidesheets and the like may be preferred. The thickness of the substrate maybe from about 10 micrometers to over about 10 millimeters with anrepresentative thickness being from about 50 to about 100 micrometers,especially for a flexible plastic substrate and from about 1 to about 10millimeters for a rigid substrate such as glass plate or silicon wafer.

The gate electrode can be a thin metal film, a conducting polymer film,a conducting film made from conducting ink or paste, or the substrateitself can be the gate electrode, for example heavily doped silicon.Examples of gate electrode materials include but are not restricted toaluminum, gold, chromium, indium tin oxide, conducting polymers such aspolystyrene sulfonate-doped poly(3,4-ethylenedioxythiophene)(PSS-PEDOT), conducting ink/paste comprised of carbon black/graphite orcolloidal silver dispersion in polymer binders, such as ELECTRODAGTMavailable from Acheson Colloids Company. The gate electrode layer can beprepared by vacuum evaporation, sputtering of metals or conductive metaloxides, coating from conducting polymer solutions or conducting inks byspin coating, casting or printing. The thickness of the gate electrodelayer ranges for example from about 10 to about 200 nanometers for metalfilms and in the range of about 1 to about 10 micrometers for polymerconductors.

The source and drain electrode layers can be fabricated from materialswhich provide a low resistance ohmic contact to the semiconductor layer.Typical materials suitable for use as source and drain electrodesinclude those of the gate electrode materials such as gold, nickel,aluminum, platinum, conducting polymers and conducting inks. Typicalthicknesses of source and drain electrodes are about, for example, fromabout 40 nanometers to about 10 micrometers with the more specificthickness being about 100 to about 400 nanometers.

The gate dielectric layer generally can be an inorganic material film oran organic polymer film. Illustrative examples of inorganic materialssuitable as the gate dielectric layer include silicon oxide, siliconnitride, aluminum oxide, barium titanate, barium zirconium titanate andthe like; illustrative examples of organic polymers for the gatedielectric layer include polyesters, polycarbonates, poly(vinyl phenol),poi yimides, polystyrene, poly(methacrylate)s, poly(acrylate)s, epoxyresin and the like. The thickness of the gate dielectric layer is, forexample from about 10 nanometers to about 500 nanometers depending onthe dielectric constant of the dielectric material used. Anrepresentative thickness of the gate dielectric layer is from about 100nanometers to about 500 nanometers. The gate dielectric layer may have aconductivity that is for example less than about 10⁻¹² S/cm.

The gate dielectric layer, the gate electrode, the semiconductor layer,the source electrode, and the drain electrode are formed in any sequencewith in embodiments the gate electrode and the semiconductor layer bothcontacting the gate dielectric layer, and the source electrode and thedrain electrode both contacting the semiconductor layer. The phrase “inany sequence” includes sequential and simultaneous formation. Forexample, the source electrode and the drain electrode can be formedsimultaneously or sequentially. The composition, fabrication, andoperation of field effect transistors are described in Bao et al., U.S.Pat. No. 6,107,117, the disclosure of which is totally incorporatedherein by reference.

For a p-channel OTFT, the source electrode is grounded and a biasvoltage of generally, for example, about 0 volt to about −80 volts isapplied to the drain electrode to collect the charge carrierstransported across the semiconductor channel when a voltage of generallyabout +20 volts to about −80 volts is applied to the gate electrode.

The semiconductor layer comprising the Compound in an OTFT devicegenerally exhibit a field-effect mobility of greater than for exampleabout 10⁻³ cm²/Vs (square centimeter per Volt per second), and an on/offratio of greater than for example about 10³. On/off ratio refers to theratio of the source-drain current when the transistor is on to thesource-drain current when the transistor is off.

The invention will now be described in detail with respect to specificrepresentative embodiments thereof, it being understood that theseexamples are intended to be illustrative only and the invention is notintended to be limited to the materials, conditions, or processparameters recited herein. All percentages and parts are by weightunless otherwise indicated. As used herein, room temperature refers to atemperature ranging for example from about 20 to about 25 degrees C.

EXAMPLE 1 Synthesis and properties of Polymer (13) (a)2,8-Bis(2-thienyl)-5,11-didodecylindolo[3,2-b]carbazole (Scheme 3)

ALIQUAT™336 (0.6 g), 2-thiopheneboronic acid (0.921 g, 7.2 mmol),2,8-dibromo-5,11-didodecylindolo[3,2-b]carbazole (2.252 g, 3 mmol), 2MNa₂CO₃ solution (7.5 mL, 15 mmol), Pd(PPh₃)₄ (72 mg, 0.06 mmol) andtoluene (10 mL) were added into a 50 mL flask. The mixture was heated togentle reflux and maintained for 48 h. The reaction mixture was cooleddown, organic layer separated, dried, and filtered. The toluene solutionwas passed through a silica gel column and the solvent was removed.Recrystallization from toluene gave the title compound as a yellowsolid. Yield: 1.476 g (61%).

(b) Polymer (13) (Scheme 3)

FeCl₃ (0.45 g, 2.77 mmol) and chlorobenzene (10 mL) were added to theflask and protected by argon.2,8-bis(2-thienyl)-5,11-didodecylindolo[3,2-b]carbazole (0.50 g, 0.66mmol) in chlorobenzene (10 mL) was added dropwise to above solution. Thereaction mixture was stirred at for 24 h and then poured into methanol(100 mL). The solid was filtered off and washed with water and methanol.The solid was stirred in ammonia solution for 24 h. The solid was washedoff and washed with water and methanol. The solid was collected in thethimble and was subjected to Soxhlet extraction with heptane for 24 h.The polymer was then dissolved by refluxing chlorobenzene. The solutionwas concentrated and added to methanol to afford a solid polymer, whichwas dried under a reduced pressure. Yield: 0.114 g (23%).

(c) OTFT Fabrication and Characterization

A top-contact thin film transistor configuration as schematicallyillustrated, for example, in FIG. 3 was selected as our test devicestructure. The test device was built on an n-doped silicon wafer with athermally grown silicon oxide layer with a thickness of about 110nanometers thereon, and had a capacitance of about 30 nF/cm²(nanofarads/square centimeter), as measured with a capacitor meter. Thewafer functioned as the gate electrode while the silicon oxide layeracted as the gate dielectric. The silicon wafer was first cleaned withisopropanol, argon plasma, isopropanol and air dried, and then immersedin a 0.1 M solution of octyltrichlorosilane (OTS-8) in toluene at 60° C.for 20 min. Subsequently, the wafer was washed with toluene, isopropanoland air-dried. A solution of polymer (13) dissolved in chlorobenzene(0.5 percent by weight) was first filtered through a 1.0 micrometersyringe filter, and then spin-coated on the OTS-8-treatet silicon waferat 1000 rpm for 60 seconds at room temperature. This resulted in theformation of a semiconductor layer with a thickness of 20-50 nanometerson the silicon wafer, which was then dried in a vacuum oven at 80° C.for 5-10 h. Subsequently, gold source and drain electrodes of about 50nanometers in thickness were deposited on top of the semiconductor layerby vacuum deposition through a shadow mask with various channel lengthsand widths, thus creating a series of transistors of various dimensions.

The evaluation of transistor performance was accomplished in a black box(that is, a closed box which excluded ambient light) at ambientconditions using a Keithley 4200 SCS semiconductor characterizationsystem. The carrier mobility, μ, was calculated from the data in thesaturated regime (gate voltage, V_(G)<source-drain voltage, V_(SD))according to equation (1)I _(SD) =C _(i)μ(W/2L)(V _(G) −V _(T))²  (1)

where I_(SD) is the drain current at the saturated regime, W and L are,respectively, the semiconductor channel width and length, C_(i) is thecapacitance per unit area of the gate dielectric layer, and V_(G) andV_(T) are, respectively, the gate voltage and threshold voltage. V_(T)of the device was determined from the relationship between the squareroot of I_(SD) at the saturated regime and V_(G) of the device byextrapolating the measured data to I_(SD)=0.

The transfer and output characteristics of the devices showed thatcompound was a p-type semiconductor. Using transistors with a dimensionof W=5,000 μm and L=90 μm, the following average properties from atleast five transistors were obtained:

Mobility: 1.0×10⁻³ cm²/V.s

On/off ratio: 10⁵.

The mobility and current on/off ratio achieved by embodiments of thepresent thin film transistor devices are useful for various applicationsin electronics such as for example electronic paper.

1. An electronic device comprising a compound comprising at least oneoptionally substituted indolocarbazole moiety and at least one divalentlinkage, wherein the at least one divalent linkage is connected to theat least one optionally substituted indolocarbazole moiety through aperipheral carbon atom; and wherein the at least one divalent linkage isindependently selected from the group consisting of the followingstructural units which are optionally substituted:

—O—, and a combination thereof, wherein X is selected from the groupconsisting of C(R′R″), O, S, Se, NR′, and Si(R′R″), and wherein R′ andR″ are independently selected from the group consisting of an alkylgroup, a cyclic aliphatic group, an aryl group, an alkylaryl group, anarylalkyl group, a heteroatom-containing group, a halogen and a mixturethereof; and Y is a carbon atom or a nitrogen atom.
 2. The electronicdevice of claim 1, wherein the at least one divalent linkage isconjugated.
 3. The electronic device of claim 1, wherein there is onlyone type of the optionally substituted indolocarbazole moiety.
 4. Theelectronic device of claim 1, wherein the at least one optionallysubstituted indolocarbazole moiety is substituted by one or moresubstituents independently selected from the group consisting of analkyl group, a cyclic aliphatic group, an aryl group, an alkylarylgroup, an arylalkyl group, a heteroatom containing group, a halogen, anda mixture thereof.
 5. The electronic device of claim 1, wherein the atleast one optionally substituted indolocarbazole moiety is independentlyselected from the structures (A), (B), (C), (D), (E), (F) and (G):

wherein for each of the structures (A) through (G), each R isindependently selected from the group consisting of a hydrogen, an alkylgroup, a cyclic aliphatic group, an aryl group, an alkylaryl group, anarylalkyl group, and a heteroatom-containing group; and wherein each ofthe structures (A) through (G) is optionally peripherally substituted.6. An electronic device comprising a small molecule compound comprisingat least one indolocarbazole moiety and at least one divalent linkage,wherein the at least one indolocarbazole moiety is optionallyperipherally substituted; and wherein the at least one divalent linkageis independently selected from the group consisting of the followingstructural units which are optionally substituted:

—O—, and a combination thereof, wherein X is selected from the groupconsisting of C(R′R″), O, S, Se, NR′, and Si(R′R″), and wherein R′ andR″ are independently selected from the group consisting of an alkylgroup, a cyclic aliphatic group, an aryl group, an alkylaryl group, anarylalkyl group, a heteroatom-containing group, a halogen and a mixturethereof; and Y is a carbon atom or a nitrogen atom.
 7. The electronicdevice of claim 6, wherein the at least one divalent linkage isconjugated.
 8. The electronic device of claim 6, wherein the smallmolecule compound has a plurality of the at least one optionallysubstituted indolocarbazole moiety.
 9. The electronic device of claim 6,wherein the electronic device comprises a thin film transistor, whereinthe thin film transistor comprises a semiconductor layer including thesmall molecule compound.